This application claims priority of Argentina Application No. P 02 01 00055 filed Jan. 9, 2002 in the Republic of Argentina Patent Office.
The instant invention relates to a process for manufacturing a high strength container, particularly an aerosol container, and to a container obtained by such process.
The main object of the invention is a process for shaping aerosol containers from an aluminum disk, affording novel features due to a substantial change in the production concept for shaping a cylindrical hollow body, of planar circular base, from a deformation of the latter by high speed impact pressing at room temperature which allows, within a die, the cold extrusion of the disk material, the material flowing in a direction opposite to that of disk pressing.
Another object of the invention is a process allowing savings in the container material, by a change of the shape at the lower portion or base of the cylindrical body in order to afford high inner pressure strength with a uniform thickness to the side wall as well as to said base or bottom, this being attained during the material extrusion caused by the disk pressing.
Another object of the invention is a process for obtaining a cylindrical hollow body by pressing the aluminum disk material allowing the shaping of a low thickness bottom, without material concentration at the joint with the container side wall, thus eliminating unnecessary further stresses to which containers are subjected to during the further step of forming the convex traditional bottom.
Still another object of the invention is a process for obtaining a lower cost container due to material savings and easy to manufacture in conventional production lines, having high pressure strength and allowing, due to the bottom shape, a different exposition due to its concave bottom.
Finally, a further object of the invention is a container obtained through the mentioned process, having a concave bottom, a uniform wall thickness and high inner pressure strength due to a particular way of distributing stresses.
Various products are known which are packaged with a pressurized gas to be transferred in a spray form through a valve device operated by hand and incorporated to the container. Among them, the so-called aerosols are of widespread use and generally have cylindrical similar shapes with valve devices provided with pulsators at the top and mounted on a closing cover of the cylindrical container, made of sheet metal material and having a characteristic convex support base and the most prominent contour directed towards the upper side of the virtual planar base of the cylindrical container.
This convex shape has been maintained in this kind of containers for pressurized products, such as aerosols, since they have at the base a perimetral edge or region for supporting the container firmly, and establishes an increase in the surface for affording a higher resistance to the pressure inside the containers.
Manufacturing of containers is carried out conventionally by embedding, particularly of aluminum or tin metal sheets or disks in dies whose shape and diameter correspond to the shape of the final part, which for aerosols are cylindrical with planar circular base. In conventional embedding operations a male forcing the metal disk inside the die is used so as to obtain the desired shape. Following this conventional embedding operation in present production lines, the planar circular base cylindrical parts are subjected to successive finishing steps, among them the shaping of a convex bottom, a tapered shape at the top and a curl for fixing the valve device (FIG. 6).
The conventional step of preparing the convex bottom is carried out by means of a punch frontal blow, thus attaining the desired bottom transverse profile, which deforms the planar base of the cylindrical body according to the vertical axis thereof. FIG. 5 shows schematically a container (e) of this kind, upon termination of the shaping steps and shows a conventional bottom (f) allowing the vertical support of the container.
Deformation of the disk or plate during the embedding operation for obtaining the circular base (b) cylindrical body (c) determines an improper distribution of material in said base (b), as may be seen in FIG. 4, with higher material accumulation at the annular and perimetral region (z) of the base (b) and the rear frontal blow for shaping the convex bottom (f) causing that the side walls or wall (p) of the body (c) support this stress, particularly when the material is aluminum. Material distribution once the bottom (f) is formed by means of a frontal blow is not homogeneous as may be seen in FIG. 6.
The following is a table including percentages corresponding to containers of different diameters and heights indicating the concentration in said bottom (f) so as to have an idea of the material distribution in aluminum containers when these are manufactured with conventional methods or processes:
In order to obtain an aerosol high strength container allowing a different stress distribution, high inner pressure resistance and material savings, the instant invention proposes a process for shaping this kind of containers including, as main feature, forming a cylindrical hollow body having a concave base projecting outside the body thus attaining a higher resistance to strain pressure.
With the proposed process a container as mentioned is obtained, wherein 85% of the direct manufacturing costs are related to aluminum, savings of 30% in connection with the material, which means, approximately, a saving of 25% in the costs of the container.
The process for carrying out the steps of deforming the disk for its extrusion requires the inclusion of prior treatment of the disk in order to obtain good pressing and extrusion thereof and further incorporating the conventional steps of turning and surface treatment of the hollow body obtained through extrusion for it further coloring and labeling, as well as for its tapering and forming the curl for fixing the valve cover.
The invention also relates to the container obtained with the above process. The main features of the container are its low thickness and its change in the bottom shape, implying high resistance to internal pressure. Further, as a consequence of the shape change, the appearance of the container is different from the conventional position, such as support cover or accessories allowing its horizontal positioning.
Finally, the advantages of the container obtained through the process of the invention are: a) savings in aluminum material and lower cost; b) manufacture in conventional production lines; c) higher capacity of the container and reduced costs; d) the change in shape allows subjecting the container to lower stresses during manufacturing allowing reduced thickness of its wall, and e) easy application of internal coatings.